This invention relates to devices for controlling the flow of a medium through a conduit, and more specifically, to a nozzle damper assembly for controlling as well as measuring the flow of a gaseous medium through a duct.
It has long been known in the prior art to provide devices operable for controlling the flow of a medium through a conduit. More specifically, the prior art is replete with examples of various types of devices that have been used heretofore to effect control over the flow of a medium through a conduit. In this regard, in many instances discernible differences of a structural nature can be found to exist between individual ones of the aforesaid devices. The existence of such differences is, in turn, attributable for the most part to the diverse functional requirements that are associated with the individual applications in which such devices are designed to be employed. For instance, in the selection of the particular type of device that is to be utilized for a specific application, one of the principal factors to which consideration must be given is that of the nature of the medium, the flow of which is to be controlled by the device. Gaseous mediums are one such type of medium wherein there is a need to control the flow thereof through a conduit. Furthermore, the air flow to a pulverizer as well as the air flow to other forms of equipment that are utilized in power generation systems are representative of applications in which there is a need to effect control over the flow of a gaseous medium as well as a need in some instances to effect, in addition, measurements of the flow of the gaseous medium.
By way of exemplification and not limitation, one particular type of flow control device heretofore known in the prior art forms the subject matter of U.S. Pat. No. 3,749,115. As set forth in U.S. Pat. No. 3,749,115, industrial plants commonly employ ducts for conducting various types of gaseous fluids. Moreover, where it is desired to regulate or to terminate the flow of such fluids through a duct, dampers are employed. In large ducts of extended lateral dimensions a plurality of aligned, mutually cooperating dampers are employed to close the duct passage. A totally effective seal of the duct passage is not possible in actual practice solely by means of a cooperation between adjacent dampers due to the difficulty in achieving a fluid tight metal-to-metal seal. This is caused principally by the fact that warpage of the members normally occurs when the dampers are disposed in a high temperature environment or particulate matter is deposited on the mating surfaces of adjacent members when they are disposed in an unclean atmosphere thereby preventing the mating surfaces from seating properly. A combination of both conditions prevails in some applications such as, for instance, the combustion gas duct of vapor generators.
Therefore, in accordance with the teachings of U.S. Pat. No. 3,749,115, a flow damper apparatus of relatively inexpensive construction is provided that is effective to positively prevent the flow of controlled gaseous fluid in a duct passage. To this end, the dampers are formed as hollow bodies and are connected to a source of sealing fluid. In addition, oppositely spaced seal plates disposed along the edges of the damper bodies form spaces between adjacent dampers into which sealing fluid is directed thereby forming a fluid seal between the upstream and downstream sides of the damper apparatus.
By way of exemplification and not limitation, another prior art type of flow control device forms the subject matter of U.S. Pat. No. 3,854,500. More specifically, U.S. Pat. No. 3,854,500 is directed to large fluid shut-off valves of the gate type. Gate valves, as set forth in U.S. Pat. No. 3,854,500, are widely used in the control of large fluid flows because of the desirable flow characteristics produced by their unimpeded flow-through construction. The typical gate valve consists merely of a valve body with a through passage for the flow of liquid and a transverse track or seat which permits and guides the movement of a plate-like gate for flow blocking. A large number of problems are inherent, however, in the operation of such gate valves.
To this end, in accordance with the teachings of U.S. Pat. No. 3,854,500 a gate valve is provided that is designed to overcome the cocking, warping, linear expansion friction due to high pressures, and fluid leakage problems experienced by the prior art. Furthermore, the nature of the construction of the gate valve of U.S. Pat. No. 3,854,500 is such that the driving or closing means is connected to the gate by a centrally located pivotal connection, thereby allowing closing and opening of the valve without blade cocking. Moreover, a multiparallel gate is proposed to reduce the size of the individual gates thereby reducing the large thermal warp observed in one large gate. Gates of reduced size also reduce the overall linear temperature expansion observed in large gates, thus allowing smaller clearances and reduced gas leakage. To overcome the friction problem resulting from high pressures pressing on the gate valve, the nature of the construction of the gate valve of U.S. Pat. No. 3,854,500 is such that an air cushion support lifts the gate against the high pressure and allows low friction opening of the gate. This support consists of pressurized air which is admitted to a series of end-to-end grooves whose openings face upstream and face the edge portion of the downstream face of the gate. Pressurized air is admitted to each groove by valves triggered by the movement of the gate. Finally, the gate sealing means consists of a plurality of longitudinal grooves arranged in the valve body facing upstream and parallel to the direction of movement of the gate. The gate blade's edges slide along and overlie the grooves creating close metal-to-metal contact and a labyrinthian seal.
By way of exemplification and not limitation, yet another prior art type of flow control device forms the subject matter of U.S. Pat. No. 3,889,552. More specifically, U.S. Pat. No. 3,889,552 is directed to an actuating device for multiple dampers. As set forth in U.S. Pat. No. 3,889,552, it is known that during low load operation of large steam generators, vibration of the induced draft fan or gas recirculation fan is sometimes encountered. In this regard, the inlets to these fans are controlled by a multitude of small coacting dampers extending across the width of the inlet ducts. Furthermore, it has been determined that one way of reducing fan vibration problems is to have a fine control over the damper positions during low load operation, and to allow flow through only selective dampers.
To this end, in accordance with the teachings of U.S. Pat. No. 3,889,552 a single actuating device is provided which permits initial opening of one or more of a plurality of dampers, while the other dampers remain in their closed position. The actuating device further accomplishes full opening of all of the dampers simultaneously. The actuating device comprises a linkage arrangement having a dogleg link therein for accomplishing the above.
Yet still another prior art form, by way of exemplification and not limitation, of flow control device forms the subject matter of U.S. Pat. No. 4,182,359. More specifically, U.S. Pat. No. 4,182,359 is directed to a slide gate damper. As set forth in U.S. Pat. No. 4,182,359 it has been known in the prior art that in large ducts gate valves are often used for closing the ducts from flow therethrough. Such gate valves are positioned on one side of the duct, and are moved transversely so they extend entirely across the span of the duct when in a closed position, with the leading edge seating in an end frame. Moreover, when the duct is conveying hot gases, the large span of the gate can warp, causing proper seating problems in the end frame. Also, when the gases are dust laden, the dust can become trapped in the end frame, preventing proper seating of the gate valve. Further, if there is a need for a concentric pipe, or other control obstruction in the large duct, it is presently impossible to position a gate valve at this location.
To this end, in accordance with the teachings of U.S. Pat. No. 4,182,359 a double gate valve arrangement is provided with the gates being positioned diametrically opposite each other, so they close and seat in the middle of the duct. In addition, the leading edge of each gate is tapered back from the side edges so that they will properly seat even if they are slightly warped from the seat. Finally, an air seal is provided to prevent any leakage through the gate.
Although flow control devices constructed in accordance with the teachings of the four issued U.S. patents to which reference has been made heretofore have been demonstrated to be operative for the purpose for which they have been designed, there has nevertheless been evidenced in the prior art a need for such flow control devices to be further improved. For example, desirably such flow control devices should possess the capability of being able to not only control but also of being able to simultaneously measure the flow of a gaseous medium through a duct. Moreover, there has been evidenced in the prior art a need for a new and improved flow measuring and control device which would permit a wider range of flow rates to be handled than that which is possible with a fixed throat area device such as a venturi or flow nozzle. Namely, whereas prior art forms of flow control devices often times have been limited to a turndown of 4 to 1, there has been evidenced in the prior art a need for a new and improved measuring and control device with which one would be able to achieve a much wider range of turndown ratios, e.g., on the order of up to 40 to 1. In addition, there has been evidenced in the prior art a need for a new and improved flow measuring and control device with which one is capable of achieving a turndown ratio of up to 40 to 1 and wherein furthermore it is possible by varying the throat area thereof to maintain virtually a constant differential pressure throughout this entire turndown ratio of up to 40 to 1. Another characteristic which such a new and improved flow measuring and control device desirably should possess is that it be relatively short in length so as to, therefore, facilitate its installation in a duct. It is to be noted in this regard that the ducts in which such a new and improved flow measuring and control device would be designed to be used commonly would be on the order of five feet by five feet, six feet by six feet, etc., depending upon the nature of the specific application in which the new and improved flow measuring and control device is being employed. Yet another characteristic which such a new and improved flow measuring and control device desirably should possess is that it be relatively simple in construction. To this end, such a new and improved flow measuring and control device should embody, to the extent possible, a modular form of construction so as to, therefore, facilitate the manufacture, transport and installation thereof. Thus, by way of summarization a need has been evidenced in the prior art for such a new and improved flow measuring and control device that is suitable for use for purposes of effectuating the simultaneous measurement and control of the flow of a gaseous medium such as air through a duct enroute to a pulverizer or to some other forms of equipment of the type that are commonly employed in power generation systems.
It is, therefore, an object of the present invention to provide a new and improved flow control device suitable for use for purposes of effectuating control over the flow of a gaseous medium through a conduit.
It is a further object of the present invention to provide such a flow control device that possesses the capability of being able to not only control the flow but also the capability of being able to simultaneously measure the flow of a gaseous medium through a conduit.
It is another object of the present invention to provide such a flow measuring and control device that is particularly suited for use in measuring and controlling the air flow entering exhauster-type pulverizers.
It is still another object of the present invention to provide such a flow measuring and control device that is particularly suited for use in measuring and controlling the air flow entering forms of equipment which are employed in power generation systems other than exhauster-type pulverizers.
A further object of the present invention is to provide such a flow measuring and control device particularly suited for use in measuring and controlling the flow of a gaseous medium through a conduit which is characterized in that it is possible therewith to handle a wider range of flow rates than that which is possible with a fixed throat area device such as a venturi or flow nozzle.
A still further object of the present invention is to provide such a flow measuring and control device particularly suited for use in measuring and controlling the flow of a gaseous medium through a conduit which is characterized in that it possesses the capability of enabling a much wider range of turndown ratios to be attained therewith, e.g., up to 40 to 1, as contrasted to prior art forms of flow control devices which oftentimes have been limited to turndown ratios of 4 to 1.
A still another object of the present invention is to provide such a flow measuring and control device particularly suited for use in measuring and controlling the flow of a gaseous medium through a conduit which is characterized in that it possesses the capability of being either manually operated or remotely operated.
Yet a further object of the present invention is to provide such a flow measuring and control device particularly suited for use in measuring and controlling a gaseous medium through a conduit which is characterized in that it is relatively short in length so as to, therefore, facilitate its installation in a conduit.
Yet another object of the present invention is to provide such a flow measuring and control device particularly suited for use in measuring and controlling the flow of a gaseous medium through a conduit which is characterized in that it embodies a modular form of construction thereby facilitating the manufacture, transport and installation thereof.
Yet still another object of the present invention is to provide such a flow measuring and control device particularly suited for use in measuring and controlling the flow of a gaseous medium through a conduit which is equally applicable for employment in new installations as well as in retrofit applications.